This invention relates generally to the direct reduction of iron oxide materials to produce metallic iron in a solid state, such as sponge iron or metallized pellets. "Metallized", as used throughout this specification does not means coated with metal, but means nearly completely reduced to the metallic state, i.e., always in excess of 75% metal, and usually in excess of 85% metal in the product. Such metallized pellets are well suited as feed material to steelmaking furnaces such as an electric arc furnace. It is desirable to control the carbon content of such pellets to any specified level between 0 and 4%. For electric furnace operation, this level usually varies between 0.8 and 2%.
In the operation of a shaft furnace, raising the operation temperature in the furnace above the normal operating temperature of about 1400.degree. F causes an increase in production, but a concomitant loss of carbon in the product. Thus it is also desirable to control the carbon content of the metallized iron pellet product within certain limits while increasing the operating temperature of the furnace while increasing the production rate.
I have found that by injecting methane or methane-containing gas at certain specified locations in a direct reduction shaft furnace, I can increase the operating temperature of the furnace as much as 300.degree. F, and increase the production capacity while controlling the carbon content of the product between 0 and 4%.